The present invention relates in general to sensors which utilize optical fibers, and in particular to a new and useful arrangement for the jaws in a microbend sensor which squeeze an optical fiber to modulate a light signal passing therethrough.
Optical fibers or cables are known which can be used to convey light between a light source and a light detector. Light in the fiber can be modulated by bending or otherwise distorting the fiber. This produces a modulated signal which can be picked up and processed by the light detector.
In a microbend sensor, for example of the type used in a vortex shedding flowmeter, a sensing body or beam extends into a flow of fluid for which flow rate is to be measured. By positioning a bluff or obstruction in the flowing fluid, vortices are formed by fluid passing over and being shed from the bluff. The vortices move the beam as they pass it. The frequency of the vortices can be used as a measurement of the flow rate.
In a microbend sensor, the sensor beam or body has an end which is mechanically connected to one corrugated jaw of a two jaw arrangement. The other corrugated jaw is fixed in a housing of the sensor and a fiber optic cable is held between the corrugated jaws. The movement of the beam causes squeezing and releasing of the fiber optic cable. Light passing through the cable is thus modulated at a frequency corresponding to the passage of vortices in the fluid flow. In such microbend sensors, care should be taken to avoid overstressing of the optical fiber. This can reduce fiber life. The fiber can be overstressed not only during the sensing operation, but also during a calibration step where the jaws are moved together by a selected amount in an initial calibration step. The jaws can inadvertently be pushed too closely together thereby damaging the optical fiber.